Screw pump unit



Filed April 13, 1959 2 Sheets-Sheet 1 wwi E. WILDHABER SCREW PUMP UNITSept. l, 1964 2 Sheets-Sheet 2 Filed April 13, 1959 IN V EN TOK:

United States Patent O 3,146,723 SCREW PUMP UNIT Ernest Wildhaber, 124Summit Drive, Brighton, N.Y. Filed Apr. 13, 1959, Ser. No. so6,117Claims. (Cl. 103-118) The present invention relates to screw pumpscompn'sing at least a pair of interengaging screws rotatable on parallelaxes and adapted to displace fluid in the direction of said axes.

A line of screw pumps must include provision for displacing a great manydifferent volumes per minute. This is ordinarily accomplished with agreat many different screw diameters, that require a great manydifferent cutters for producing them.

One object of the present invention is to save cost by using acomparatively small number of screw diameters and attaining the manyrequired displacement volumes by running the pumps of each diameter atmany different speeds. A further object is to provide pump units ofgiven screw diameters and lead driven from a constant speed motorthrough gear pairs, and to avoid using fiexible couplings by crowning atleast one member of the gear pair.

A still other object is to provide a pump unit driven by a crownedexternal gear meshing with an internal gear; and a pump unit where thedrive can be disconnected without displacing either the motor or thepump on their base.

A further aim is to provide a screw pump unit having a high-speed motorof low weight and moderate cost and a gear reduction with external andinternal gear to attain a suitable pump speed, and to do so withoutadding to the number of bearings.

Another object is to devise a screw pump unit that can be run atrelatively high speed without danger of cavitation, where the fluid hasa larger axial intake velocity than attainable by suction, and where apropeller is added to the positive displacement screws to impart initialpressure on the fluid, to enable it to attain the high intake velocityat the screws.

Other objects will appear in the course of the specification and in therecital of the appended claims.

In the drawings:

FIG. 1 is a plan View of a screw pump unit constructed according to thepresent invention, the screw-carrying portion being shown in axialsection, and the motor being indicated fragmentarily.

FIG. 2 is an axial section corresponding to FIG. l and taken at rightangles thereto.

FIG. Za is a fragmentary section of one member of the reduction gearpair shown in FIG. 2, illustrating crowning, the section being takenalong a mean cylindrical surface laid through the teeth coaxial withsaid one member, and developed into a plane.

FIG. 3 is a diagrarnmatic side view of the screw pump unit of FIGS. 1and 2, at a smaller scale.

FIG. 4 is a cross section of the interengaging screws shown in FIGS. land 2.

FIG. 5 is a diagram showing the intake area of the propeller shown inFIGS. 1 and 2.

FIG 6 is a fragmentary view and axial section showing a modified gearreduction in a unit otherwise corresponding to FIGS. 1 and 2.

FIG. 7 is a fragmentary end View of a gear pair with external andinternal gear of small tooth number difference, illustrating aditficulty existing with the conventional design.

FIG. 8 is a similar end view of the gear pair modified in accordancewith the invention to overcome said difi iculty, so that it can be usedin the present screw pump unit.

In the embodiments illustrated a central power screw &146323 PatentedSept. 1, 1954 20 engages a pair of screws 21, 21', all rotatable onparallel axes. To achieve thrust balance, each screw contains a righthand half and a left hand half. The shape of the screws themselves isknown, and any known combination and screw number may be used. Onrotation the screws may displace fluid from the outer ends towards thecenter, to be discharged through opening 22 (FIG. 2). The intake isthrough an opening 23 and thence to the ends of the screws.

In establishing a line of screw pumps it is important to provide only asmall number of different screw diameters, and to have only one lead fora screw of given diameter. In this way only a small number of theexpensive tools are required to produce the screw shapes, and a smallnumber of stock parts. Also a small number of different machine set-upsare sutficient.

Yet it is mandatory to offer a great many delivery volumes per minutewhile preferably retaining a constant motor speed.

In accordance with the invention a motor of preferably high speed isprovided, to save in weight and cost, and a number of different gearreductions are used with each pump diameter to provide the great numberof delivery volumes.

The invention provides a gear reduction that has the double purpose ofchanging the speed and of giving flexibility of assernbly. Suchflexibility is now commonly attained with flexible couplings, thatusually comprise external gear members with crowned teeth meshing withconcentric internal gear members with straight teeth, the tooth numbersbeing the same on the external and internal members.

In accordance with the invention crowned teeth are provided on onemember of the reduction gear pair, whereby the desired flexibility isachieved without a flexible coupling.

In the embodiment illustrated the reduction gear comprises an internalgear 24 removably secured to a flange member 25 by screws 26. Member 25is rigidly secured to the shaft 27 of the pump screw 20, as by splines28. Internal gear 24 meshes with an external pinion 39 rigidly securedto the motor shaft 31, that projects from motor 32 and that isjournalled in bearings within the motor housing.

To displace fluid from the ends towards the center 29 of the screws, thedrive of screw 20 should be in the direction of arrow 33 with the handof thread shown. Pinion 30 preferably contains helical teeth 45 of ahand opposite to the hand of screw 20, so that when driving in thedirection of arrow 33 it draws the gear 24 and flange member 25 towardsthe pinion.

On its left side face the pinion 30 has a slightly conical contactsurface 35 adapted to contact a conical contact surface 36 provided onflange member 25. In operation the contact surfaces 35, 36 roll andsomewhat slide on each other and completely balance the end thrust ofthe gear teeth.

A disk 37 is tightly secured to the right end face of gear 24 by a nut38 threading onto the gear. It contacts the plane end face 40 of thepinion 30. Disk 37 may be thin and elastic and shaped to exert pressureon end face 40. It forms a lubricant pocket at the lower end 41 ofinternal gear 24. If desired further scaling means may be provide. Withthe described arrangement the pinion 40 is preferably placed verticallyabove the gear center.

It should be noted that the internal gear 24 is out in the open and isreadily accessible. It can be detached from the flange member 25 byremoving the screws 26, and without displacing either motor 32 or purnp43 on their common base 44, FIG. 3.

In mounting the motor 32 and pump 42 on base 44-, the two have to bealigned with each other so that their &146323 axes are as nearlyparallel as readily feasible. Involute gears are known to be insensitiveto changes in center distance. The gears are thus entirely insensitiveto small horizontal or vertical displacements. Displacement `in theplane of the axes changes the backlash, of which there is enough forsmall mounting displacements. Small displacements at right angles tosaid plane do not even aliect the backlash.

One of the two members of the gear pair 24, 30 is provided with crownedteeth. Crowning is preferably applied to the pinion. The sides 45', 45"of the teeth 45 (FIG. Za) are longitudinally convex in developmentinstead of being straight. This is known to enable them to mesh properlyeven if their aXes are not exactly parallel.

Accordingly a crowned gear pair fulfills the double purpose of providinga gear reduction and of giving son-ie flexibility as to parallelism. Aflexible coupling is dispensed with as the invention also provides readydisconnection, and a saving in cost is made.

Shaft 27 of pump screw 20 is rotatably mounted in bearings 46, 47 heldby parts 48, 50 rigidly secured to the central pump body 51 by flanges52, 53 and screws 54, 55. The shaft passes through seals 56, 57 beforereaching the bearings 46, 47, all seals being pointed out by diagonallines. Each seal 56, 57 can be tightened by turning a nut 43, accessiblefrom the outside through an opening 49.

Another aspect of the invention will now be described. in general theinvention tends to use increased rotational speeds of the screws. Thefluid then moves axially of the screws at a faster rate. As this speedexists already on the entering side of the screws it has to be providedby suction. There is however a definite known limit as to what suctioncan do.

The invention achieves increased velocities on the entering side of thescrews by putting the fluid under some initial pressure. While the screwpump provides a positive fluid displacement, a non-positive bladedrotary part is used to act on the fluid before it enters the screws, sothat the entering velocity is not caused by suetion alone. The said partis in the nature of a propeller 60 or 60' (FIGS. 1 and 2) rigidlysecured to shaft 27 as for in stance by radial pins 59. There is onepropeller for each end of the double screw 20. The two propellers 60,60' are symmetrical to one another. They are alike except for hand.

Each contains twisted blades 61 of low angle of incidence i (FIG. l), atleast at the entering or intake side. Angle at any radius within thesweep of the blades is smaller than, ordinarily less than one half ofthe lead angle at this radius that corresponds to the lead of screw 20connected with the propeller. Also a comparatively large area 62 (FIG.is swept at the entering side, so that the fluid can enter at arelatively slow velocity that can be safely attained by suction. Area 62is larger than the total area of the thread spaces of said screws (21,20, 21'). The thread spaces are the areas between the threads, boundedby the outside circles and root circles. These circles are indicated at65, 65' for screw 20.

The blades 61 are shown curved for strength, but do not necessarily haveto be curved. They may be made truly helical if desired.

The fluid is guided from the intake opening 23 towards the outer ends ofscrew 20 and to a ring-shaped guide channel 63 adjacent the respectivepropellers 60, 60', on the far side of screw 20. T hence it passesthrough the propellers 60, 60' to a space 64 or 64' immediately ahead ofthe screws, and to the screws 20, 21, 21' themselves. It moves axiallyalong the screws to center 29 and to discharge opening 22.

In spite of the gear reduction provided no bearings are added. There arethe bearings 46, 47 for rotatably mounting screw 20; and there are thebearings (not shown) within the motor housing for mounting the motorrotor and motor shaft 31. This contributes to easy assembly anddissembly.

Larger Redaction Rat'os When the gearing provides a substantially largerreduction than shown in FIG. 2, it is preferably enclosed, as shown inFIG. 6. This embodiment uses the same central part 51 and end part 48,as described, and may use the same pump screws 20, 21, 21'. The drivingpinion 30' is here however at a smaller proportion to the internal gear24'.

A split housing 66 encloses the gear pair 24', 30'. It is preferablysplit on a horizontal level into a lower and an upper half. The twohalves are hightly secured to gether by screws passing through the holes67.

The end part 50' of the screw pump is modified from the described part50 on the outside to receive housing 66. The housing holds lubricant andts tightly around the cylindrical surface 68 of end part 50'. A sealdiagrammatically indicated at 70 is provided at the hub 71 of pinion 30'and held by a ring 72. Ring 72 contains a peripheral V-shaped groove 73that is matched by a projection 74 of housing 66, to tghtly hold saidring. If desired the housing 66 nay rest on the base 44 of the unit,preferably on a somewhat yielding plate secured to said base.

In this embodiment also no bearings have been added, and some mountingflexibility is attained by crowning the teeth of the pinion 30', so thatthe reduction gear of this unit also has the function of a fiexiblecoupling.

Lm'tal'on of lnternal Gear Drive The internal gear drive is known tohave a limitation when the tooth number of the pinion is only slightlysmaller than that of the internal gear. FIG. 7 illustrates thedifficulty with a convcntional design of involute gears. Radial line 75contains the gear center 76 and pinion center 77, and also the pitchpoint 78, or instantaneous center of relative motion. The pitch pointcan be considered the contact point of the pitch circles (not shown)that move with the gear and pinion and roll on each other withoutsliding.

Conventionally the pitch point 73 is placed either midway of the workingdepth of the teeth, as shown in FIG. 7 or closer to the tooth bottom ofthe pinion. In either case interference occurs with the shown toothnumbers of 45 and 42. Pinion tooth 80 interferes with gear tooth 81 andadjacent gear and pinion teeth interfere with each other so that thetooth numbers shown in FIG. 7 are not actually feasible with theconventonal design.

FIG. 8 illustrates a way of avoiding interference in accordance with theinvention while retaining the involute tooth form best suited foraccurate manufacture and insensitive to changes in center distancePinion 82 is identical with pinion 82 of FIG. 7. The gear 83' has thesame tooth number and the same base circle 84 as the gear 83 of FIG. 7.But the center distance 76-76" is slightly increased so that the pitchpoint is shifted to a position 78' shown with exaggeration. As wellknown the straight line of action 85 passes through the pitch point andis tangent to the base circles 34, 86 of the gear and pinion. Circle 86happens to coincide With the root circle of the pinion by coincidence.85, 85' are the lines of action for opposite tooth sides. They comparewith lines of action 87, 87' in FIG. 7.

By shifting the pitch point, or instantaneous center of relative motion,towards the outside as Compared with FIG. 7, tooth interference iselininated. Pitch point 78' lies outside of the outside circle 90 of thepinion. Actually it does not take as much Shift as shown, to clear. Apitch point in position 78" is sufiicient in many cases. In either casethe outside circle 90 of the pinion is closer to the pitch point 78',78" than the inside circle 91 of the internal gear.

In this way it is possible to come close to a one to one ratio.

It should be understood that the nvention is capable of various furthermodifications and uses, and this application is intended to cover anyvariations, uses, or adaptations of the invention following, in general,the principles of the invention and including such departures from thepresent disclosure as come within known or customary practice in the artto which the invention pertans, and as may be applied to the essentialfeatures hereinbefore set forth, and as fall within the scope of theinvention or the limits of the appended claims.

I claim:

l. A screw pump unit containing a base, a screw pump and motor rigidlymounted on said base, said pump comprising at least a pair ofinterengaging screws rotatable on parallel aXes for displacing fluidaxially of said screws from an nlet side to a discharge side, aninternal gear removably Secured to one of said screws, disconnectablemeans for connectng said internal gear with said one screw andpermitting disconnection of said internal gear from said one screwwithout displacing said pump and motor on their base, said motor havinga shaft parallel to the axes of said screws, a pinion rigidly Secured tothe shaft of said motor, said pinion meshing with said internal gear andforming a reduction pair of other than one to one and of less than twoto one ratio therewith, the teeth of at least one member of said pairbeing crowned longitudinally to permit moderate rnisalignment betweenthe directions of the axes of said one screw and of said pinion withouta flexible coupling connection.

2. A screw pump unit according to claim l, wherein said pinion has atooth number at least three quarters of the tooth number of the internalgear, and wherein said internal gear is out in the open withoutenclosure, for direct access.

3. A screw pump unit according to claim 1, wherein said pinion has atooth number larger than three quarters of the tooth number of theinternal gear, wherein said gears contain involute teeth, and whereininternal tooth interference is avoided by placing the pitch point closerto the outside circle of the pinion than to the inside circle of theinternal gear.

4. A screw pump unit according to claim 1, wherein the fluid inlet sideis disposed adjacent said internal gear, wherein thrust surfaces areprovided on said pinion and on a part rigid with said internal gear forengagement with each other, and wherein said pinion and internal gearcontain helical teeth of a hand opposite to the hand of the adjacentportion of the pump screw to which said internal gear is connected, sothat the driving pressure keeps said thrust surfaces in engagement.

5. A system of screw pump units using the same standard motor speed andcomprisng a limited number of sizes for delivering a Volume per minuteselected from a much larger number of choices than the number of sizes,said units comprising gear means with crowned teeth for transmittingpower from the motor to the pump without need of a flexble coupling,said gear means comprising an internal gear and a mating externallytoothed gear of less than two to one ratio, disconnectable means forconnectng said gear means with said pump, and permitting disconnectionof said gear means from said pump, the gear ratio of said gear meansbeing selected to effect the desired delivery Volume with said standardmotor speed.

References Cited in the file of this patent UNITED STATES PATENTS1,601,750 Wildhaber Oct. 5, 1926 1,825,621 Cox Sept. 29, 1931 2,055,587Pigott Sept. 29, 1936 2,172,662 Kuhns et al Sept. 12, 1939 2,463,46OHodgknson Mar. 1, 1949 2,501,617 Roesch Mar. 21, 1950 2,581,886 RockwellJan. 8, 1952 2,592,476 Sennet Apr. 8, 1952 2,633,083 Smith Mar. 31, 19532,640,428 Houghton June 2, 1953 2,640,430 Sennet June 2, 1953 2,659,217Talbot Nov. 17, 1953 2,682,7 Shenk July 6, 1954 2,705,922 Rathman Apr.12, 1955 2,873,588 Crankshaw Feb. 17, 1959 2,880,676 Succop Apr. 7, 19592,922,294 Wildhaber Jan. 26, 1960 2,924,181 Sennet Feb. 9, 19602,949,041 Wildhaber Aug. 16, 1960 FOREIGN PATENTS 494,075 Great BritainOct. 19, 1938 OTHER REFERENCES United Shoe Machinery CorporationBrochure, April 10,1958.

1. A SCREW PUMP UNIT CONTAINING A BASE, A SCREW PUMP AND MOTOR RIGIDLYMOUNTED ON SAID BASE, SAID PUMP COMPRISING AT LEAST A PAIR OFINTERENGAGING SCREWS ROTATABLE ON PARALLEL AXES FOR DISPLACING FLUIDAXIALLY OF SAID SCREWS FROM AN INLET SIDE TO A DISCHARGE SIDE, ANINTERNAL GEAR REMOVABLY SECURED TO ONE OF SAID SCREWS, DISCONNECTABLEMEANS FOR CONNECTING SAID INTERNAL GEAR WITH SAID ONE SCREW ANDPERMITTING DISCONNECTION OF SAID INTERNAL GEAR FROM SAID ONE SCREWWITHOUT DISPLACING SAID PUMP AND MOTOR ON THEIR BASE, SAID MOTOR HAVINGA SHAFT PARALLEL TO THE AXES OF SAID SCREWS, A PINION RIGIDLY SECURED TOTHE SHAFT OF SAID MOTOR, SAID PINION MESHING WITH SAID INTERNAL GEAR ANDFORMING A REDUCTION PAIR OF OTHER THAN ONE TO ONE AND OF LESS THAN TWOTO ONE RATIO THEREWITH, THE TEETH OF AT LEAST ONE MEMBER OF SAID PAIRBEING CROWNED LONGITUDINALLY TO PERMIT MODERATE MISALIGNMENT BETWEEN THEDIRECTIONS OF THE AXES OF SAID ONE SCREW AND OF SAID PINION WITHOUT AFLEXIBLE COUPLING CONNECTION.